Generators as utilized in IDGs, APU GENs, and other similar type electrical generators for aircraft are termed "electromechanical" devices because they convert mechanical energy from the appropriate power source to electrical energy. This energy is then utilized throughout the aircraft to light lights, cook food, and power complex systems such as pilot instrumentation, radar, communications, flight computers, etc. The conversion is accomplished as the rotational mechanical energy of the engine, for example, transmits a torque to the generator rotor, through appropriate gearing, causing this rotor to spin.
This two-pole rotor has wires wound around a field pole piece making up what is termed the field coil assembly. When an electric current is passed through this rotating field coil assembly, or more specifically through the wires wound on the field pole piece, a rotating magnetic field results. This rotating magnetic field or flux, in turn, induces a field in the structure of the generator surrounding the rotor assembly known as the stator which also has wires wound around its assembly. Connections to the windings of this stator are then made to allow the electric power to be delivered to the various loads of the aircraft.
Generally, the two-pole rotor utilized in this type of generator is composed of a plurality of precision fitted parts which are bolted or welded together. While this technical approach is functionally satisfactory, a disadvantage resides in the fact that the total costs involved in producing this rotor as a result of the required precision fitting of the components as well as the necessary welding, pinning and bolting operations, is relatively high. Further, if this precision fitted unit is to be repaired, a lengthy and expensive process requiring first that the welds be cut prior to any actual repair activity beginning must be undertaken.
Conventionally, wedge portions are provided as part of the rotor assembly. These wedges are generally hollowed out or configured to the coil profile which is somewhat rounded to accommodate the large number of windings in the field coil assembly required to generate the necessary magnetic field described above. To allow for the transmission of the large torques generated by the aircraft engine in this connection, high strength axial retention bolts are utilized to bolt the shaft ends to the field pole piece. High strength radial retention bolts are utilized in turn to retain the separate field core accommodating wedges to the field pole pieces under the tremendous centrifical forces generated by the speed at which this rotor assembly spins, typically in excess of 20,000 RPM.
To aid the torque transmission capability required to allow this assembly to spin at such a high speed, an oil accommodating canister surrounding the field coil is typically welded to the ends of the shaft after assembly and then finish ground to size. A disadvantage of this approach resides in the fact that the completed unit is, at best, difficult if not impossible to repair or service and, taking into account the manufacturing steps and processes, the unit is difficult and expensive to construct.
Specifically, with regard to service and repair, the welding of the oil accommodating canister to the ends of the shaft renders the conventional two-pole rotors more or less disposable. This is because the expensive and time consuming task of cutting these welds must first be accomplished to gain access to the core assembly which is encased by the oil accommodating canister before any service or repair may begin.
If this lengthy and expensive procedure is undertaken, and the unit is repaired, additional work is usually required to regrind the grooves, known as bearing races, which allow the unit to rotate on its bearings, as they are typically out of concentricity when the unit is reassembled.
Typical examples of rotor constructions of the aforementioned type are disclosed in, for example, U.S. Pat. Nos. 4,510,679, 4,513,641, 4,562,641, 4,591,749, 4,757,603, 4,674,178, 4,625,135, 4,598,218, and 4,614,888. While each of these patents provide various approaches for constructions of a rotor, each technical approach utilizes a multi-piece shaft construction and, consequently, suffers from the above-noted disadvantages.